Rapid PSA Process,Ultra-rapid PSA Process,Rapid Pressure Swing Adsorption Process

Rapid Pressure Swing Adsorption Process

Rapid pressure swing adsorption (RPSA) is a novel gas purification technique. It was developed by the integration of the best features of gas-liquid absorption, and pressure swing adsorption (PSA). A Rapid Pressure Swing Adsorption process uses a single, double or more adsorbent beds. Which contains one or more pairs of shallow adsorbent layers. They are separated by perforated metal plates. It is the place where the gas separation takes place. Each of the adsorber vessels has a set of valves that checks the gas flow. Valve headers are used for connecting all the adsorber for gas to flow in each vessel.

Irrespective of the number of vessels each layer is more or less cyclically subjected to the following five steps:

1)Adsorption	2)Co-current Depressurization	3)Counter-current Depressurization
4)Purge	5)Repressurization

The feeding of the air (feed gas mixture) to the adsorption system is discontinued upon completion of the feed step to each bed. This process of discontinuity of feed, before passing of feed gas mixture to the next succeeding bed, is the same throughout each processing cycle. Further, recent researches have developed a new, modified process that operates by adding either a raffinate recycle phase or an extract recycle phase.

Rapid Pressure Swing Adsorption Process can be of two types Axial flow and Radial flow. Compared to Axial-flow RPSA processes, Radial-flow RPSA processes gives the advantage of a larger cross section for an equal volume of adsorbent. Thus offering a low-pressure drop for the same volumetric flow. Also a small size of adsorbent can be applied for getting the same pressure drop.

Characteristics of Rapid Pressure Swing Adsorption(RPSA):

The most remarkable feature of Rapid Pressure Swing Adsorption(RPSA) compared to conventional PSA, is with respect to air separation for oxygen production. The pressure drop per unit of bed length is an order of magnitude. While the particle diameter of the adsorbent is usually less than 0.5 mm.
It operates at fast cycle speeds, generally have total cycle times less than 20 seconds (time less than 10 sec. is also not unlikely).
Typical Rapid Pressure Swing Adsorption Processes have very short feed steps (sometime even less than 1.0 sec.)

Applications of Rapid Pressure Swing Adsorption (RPSA):
Typically used for producing oxygen in High Pressure Oxygen Concentration System for use in numerous industries including aviation and medical.

Rapid Pressure Swing Adsorption process is also a popular choice to produce low to medium purity oxygen for use in the chemical, metallurgical and environmental industries. These include enhanced combustion in burners, cupolas,and furnaces. Controlled oxidation in chemical and biochemical reactors, aquaculture, sewage treatment etc. Rapid Pressure Swing Adsorption process is also used for industrial separation of Methane, Ethylene, Nitrogen, Hydrogen, Carbon dioxide etc. using a variety of adsorbents.

Rapid Pressure Swing Adsorption Process for Production of Oxygen-Enriched Air:
An example can be given of the production process of oxygen-enriched air through the process of Rapid Pressure Swing Adsorption. The process can use just a solitary adsorber vessel to multiple adsorber vessels containing one or more pairs of shallow adsorbent layers. Which are separated by perforated metal plates The adsorbent layers consists of a sublayer of a desiccant at the feed air end. It helps in removal of water from the ambient air. Another sublayer of zeolite is applied to selectively adsorp nitrogen from the dry air. Cycle time is usually less. Consequently, the oxygen production rate from the RPSA process is more than that from a conventional pressure swing or vacuum swing adsorption process. This results into reduction in the adsorbent inventory.

The RPSA process has the capacity to remove water from the compressed feed air along with separating air into the oxygen enriched product gas. Requirement for this is that the feed air is to be compressed to at least 25 psig. So that the pressure swing drying of the compressed air can be carried out smoothly. Thus, a minimum quantity of compression energy is necessary to operate the above described RPSA process.

Limitations of Rapid Pressure Swing Adsorption (RPSA):

Studies revealed that performance got limited when adsorbent particles used were either too small or too large.
Compared to Rapid Pressure Swing Adsorption processes, conventional PSA processes, typically consumes lower power, superior bed utilization and higher product recovery.

To overcome the limitations of RPSA a new dynamic model was developed promising solution for obtaining more rapid cycles at lesser time. By constant R&d to add more features and enhance gas recovery to the rapid cycle processes State-of-the-art Ultra Rapid Pressure Swing Adsorption (URPSA) was developed.

Ultra-Rapid Pressure Swing Adsorption (URPSA)
Ultra Rapid Pressure Swing Adsorption (URPSA) is a type of Pressure Swing Adsorption (PSA) process that offers promising solution to size and portability issues for a number of applications. It is closely linked with the the development of advanced fuel cell powered vehicles and medical-grade oxygen concentrator. This is a very challenging proposition because in the numerical simulation of URPSA models, small time steps are needed to capture the process dynamics of cycle time within fractions of seconds. Another land mark was added in the PSA technology with the development of the Piston-driven ultra rapid pressure swing adsorption (URPSA) equipment.

This unique PSA technology is showing promise as a compact yet high-capacity PSA to be utilized for a wide variety of applications. In the Piston-driven ultra rapid pressure swing adsorption (URPSA) equipment, the adsorbent bed is directly connected to the cylinder where a piston moves at high frequency. Thus the processes of pressurization and depressurization in the bed are driven by mechanical piston motion. These have been able to achieve far more rapid cycles compared with the earlier pressure swing operations using valves. The cycle time has come down in the order of seconds or sub seconds. Oxygen enrichment from air went up to about 60% or higher. Other applications include recovery of carbon dioxide from a stack gas using hydrophilic and hydrophobic zeolites.

Features of Ultra-Rapid Pressure Swing Adsorption (URPSA)
A single-stage URPSA for oxygen production is capable of producing:

Oxygen purities of 85%
Large product recoveries of around 60%
Small bed-size factor of around 0.00073
High Oxygen concentration
Superior separation efficiency per unit mass of adsorbent material is achieved in the Ultra-Rapid PSA

This implies improved efficiency of separation per unit mass of adsorbent material.